/Engine/Source/Runtime/Core/Public/Math/UnrealMathUtility.h
An approximation is used that is accurate so long as InDeltaTime < 0.5 * InSmoothingTime
template<class T> static constexpr void ExponentialSmoothingApprox ( T & InOutValue, const T & InTargetValue, const float InDeltaTime, const float InSmoothingTime )